Field of the Invention
Embodiments of the present disclosure generally relate to an apparatus for connecting a neutral conductor of an electric circuit to ground through a neutral grounding component, and for monitoring the neutral grounding component. More particularly, the present disclosure relates to an improved apparatus that is operative to detect open states and shorted states in the neutral grounding component.
Discussion of Related Art
A wide variety of electric circuits comprise neutral conductors, which carry current in normal operation but are connected to ground. Connection to ground is desirable in order to prevent the accumulation of dangerous transient voltages between neutral and ground that can be hazardous to operators of equipment housing the circuitry. However, connecting neutral conductors to ground without intervening resistance may allow excessive current flow between neutral and ground, which can cause damage to circuit components. Therefore, some system connect the neutral conductor to ground across a neutral grounding resistor (NGR), the resistance of which is selected in order to limit ground current to safe levels in the event of a ground fault.
An NGR may fail in at least two ways. The NGR may enter a failed-open condition, in which the connection between neutral and ground is broken. Alternatively, the NGR may enter a failed-short condition, in which the NGR provides no resistance, and thus the neutral conductor may be shorted to ground. As noted above, it may be undesirable to have no connection between neutral and ground, and may also be undesirable to connect neutral to ground without an intervening resistance. As such, it may be desirable to monitor an NGR, in order to detect the occurrence of failed-open conditions and failed-short conditions. However, typical systems are not capable of reliably detecting failed short conditions in NGRs. Accordingly, there is a need for a neutral grounding solution that can be monitored to detect both failed-open and failed-short conditions.